In order to correctly map an earth-image on a sphere i think i need to use polar mapping with an image that uses Equirectangular projection like this:
http://planetpixelemporium.com/earth.html [planetpixelemporium.com]

However when i need to correctly map an image that uses Mercator projection , i'm lost as to what to use as cylindrical uvmapping doesn't undo the size distortions from Mercator.
Ideally i would convert the Mercator images back to equirectangular ones but i can't find a tool that does this.

Can anybody help me out?

Hi,
you'll need to look for GIS tools. http://www.bluemarblegeo.com/global-mapper/ [bluemarblegeo.com] I have used before for something similar if I remember correctly. For one image $400 might be a bit steep though. Can't remember if the trial lets you save.

http://freegeographytools.com [freegeographytools.com] might be helpful. Have a look for MicroDEM also if my memory serves me right that has a bunch of re-projection features too.

Sorry if this is a bit inprecise but it's been a while since I needed something like this.

Best of luck,
Fabian

Thanks Fabian for your help. I've tried MicroDEM but it seems to be a bit outdated, wanting to install turboPascal and what not. I remember making my first algorithms in University with turboPascal, long long time ago.

Anyway, I ended up making an approximate deformation map to convert all mercator maps as a sequence. Although not perfect in a technical sense, the results are good enough.